Every workout has a price in energy, and exercise science has spent decades measuring it. The MET — metabolic equivalent — is the unit: 1 MET is your resting burn, and every activity in the published Compendium of Physical Activities is rated as a multiple of it.
Reading the numbers
Running at 8 km/h rates 8.3 METs: a 75 kg runner burns 8.3 × 75 × 0.75 ≈ 465 kcal in 45 minutes. Brisk walking (4.3 METs) covers about half that; jump rope (11.8 METs) beats them both minute-for-minute. Body weight multiplies directly — a 90 kg person burns ~30% more than a 70 kg person in the same session.
Where the values come from
The Compendium (Ainsworth et al., 2011 update) compiles measured oxygen-consumption data across hundreds of activities; this page carries a curated 40 spanning cardio, strength, sports and everyday chores. They're averages: your running economy, terrain and skill create honest ±10–20% variance.
Gross vs net, and the pizza line
These are gross figures — the total burned during the activity, including the ~1 MET you'd have burned on the couch. Strict "extra" burn is (MET − 1) × kg × hours. The comparison line converts your burn into pizza slices (~285 kcal) and grams of body fat (~7,700 kcal/kg) — not to moralize, but because "465 kcal" lands better with a reference.
Fit it into the bigger energy picture
Exercise is one term in the daily equation. Your TDEE already bakes typical activity into its multiplier — avoid double-counting by logging workouts on top of an "active" multiplier. Walkers converting steps instead should try the steps to miles calculator.
MET values: Compendium of Physical Activities. Estimates, not measurements.